1. Field of the Invention
The present invention relates to a robot system having a robot and, in particular, it relates to a robot system having error detection function of a robot.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 2009-196030 discloses a robot controller that controls operation of a robot arm with high accuracy. In this robot controller, a sensor is incorporated into a driving section of axes of a robot arm. The robot arm is driven based on a command torque value output to this robot arm. The sensor outputs an actual detected torque value that is actually transferred to the robot arm. A computation section identifies a difference between the command torque value and the detected torque value. When the identified difference is larger than or equal to a predetermined threshold, electric power supply to the robot arm is blocked.
Japanese Unexamined Patent Publication No. 2007-301691 discloses a robot controller that comprises two sensors and two computation sections incorporated for driving axes of a robot arm. In this robot controller, the two computation sections independently estimate the command torque values output to the robot arm. When the two estimated command torque values are equal to each other, differences between the two detected torque values detected by the two sensors and the two command torque values, respectively, are identified. When the identified differences are larger than or equal to a predetermined threshold, electric power supply to the robot arm is blocked.
In the techniques disclosed in Japanese Unexamined Patent Publications No. 2009-196030 and No. 2007-301691, frictional forces in components of the robot arm such as gears and speed reducers fluctuate due to temperature changes in an operational state and disposition environment of the robot arm. The fluctuations of the frictional forces affect the robot controllers described above. For example, the larger the frictional forces are, the larger the difference between the command torque value and the detected torque value is. As a result, in order to prevent false detection, a threshold with a margin has to be set. Even when the robot arm collides with a human or an object, for example, the collision, therefore, cannot be detected with high accuracy.
The present invention has been made to solve the above problems, and it is an object of the present invention to provide a robot system that can detect error occurring in the robot system with high sensitivity and a control method thereof.